This invention relates to acylated enol derivatives of .alpha.-ketoesters and .alpha.-ketoamides which are either elastase inhibitors or are prodrugs of elastase inhibitors, useful for a variety of physiological and end-use applications.
Human neutrophil elastase has been implicated as an agent contributing to the tissue destruction associated with a number of inflammatory diseases such as chronic bronchitis, cystic fibrosis, and rheumatoid arthritis. J. L. Malech and J. I. Gallin, New Engl. J. Med., 317(11), 687 (1987). Elastase possesses a broad range of proteolytic activity against a number of connective tissue macromolecules including elastin, fibronectin, collagen, and proteoglycan. The presence of the enzyme elastase may contribute to the pathology of these diseases.
Normal plasma contains large quantities of protease inhibitors that control a variety of enzymes involved in connective tissue turnover and inflammation. For example, .alpha.-1-proteinase inhibitor (.alpha.-1-PI) is a serine protease inhibitor that blocks the activity of elastase. .alpha.-1-PI has received considerable interest because reduction in plasma levels to less than 15% of normal is associated with the early development of emphysema.
In addition to plasma derived protease inhibitors, secretory fluids, including bronchial, nasal, cervical mucus, and seminal fluid contain an endogenous protease inhibitor called secretory leukoprotease inhibitor (SLPI) that can inactivate elastase and is believed to play an important role in maintaining the integrity of the epithelium in the presence of inflammatory cell proteases. In certain pathological states .alpha.-1-PI and SLPI are inactivated by neutrophil oxidative mechanisms allowing the neutrophil proteases to function in an essentially inhibitor-free environment. For example, bronchial lavage fluids from patients with adult respiratory distress syndrome (ARDS) have been found to contain active elastase and .alpha.-1-PI that had been inactivated by oxidation.
In addition to oxidative mechanisms, neutrophils possess non-oxidative mechanisms for eluding inhibition by antiproteases. Neutrophils from patients with chronic granulomatous disease are capable of degrading endothelial cell matrices in the presence of excess .alpha.-1-PI. There is considerable in vitro evidence that stimulated neutrophils can tightly bind to their substrates such that serum antiproteases are effectively excluded from the microenvironment of tight cell-substrate contact. The influx of large numbers of neutrophils to an inflammatory site may result in considerable tissue damage due to the proteolysis that occurs in this region.
Applicants have previously determined that elastase is one of the primary neutrophil proteases responsible for cartilage matrix degeneration as measured by the ability of neutrophil lysate, purified elastase and stimulated neutrophils to degrade cartilage matrix proteoglycan. Furthermore, various kinds of peptide derivatives useful as elastase inhibitors, exerting valuable pharmacological activities, are known in the art. For example, Angelastro, M. R. et al. J. Med. Chem., 37, 4538 (1994) and European Patent Application OPI No. 0529568, inventors Peet et al., with a publication date of Mar. 3, 1993 disclose that various peptides such as valylprolylvalyl pentafluoroethyl ketones with different N-protecting groups are inhibitors of human neutrophil elastase (HNE) in vitro and in vivo and are also orally active in HNE-induced rat and hamster lung hemorrhage models.
Moreover, the art discloses that a number of different amino acid moieties are permitted at the P.sub.1, P.sub.3, P.sub.4 sites of the elastase inhibitor and that a number of N-protecting groups may be substituted while still maintaining enzyme inhibitory activity, although oral activity is noted for only some N-protecting groups. For example, Skiles, J. W. et al., J. Med. Chem., 35, 641 (1992) disclose a number of tripeptide elastase inhibitors possessing trifluoromethyl or aryl ketone residues at P.sub.1 and N-substituted glycine residues at P.sub.2. It is demonstrated that as the substituent on the P.sub.2 -glycine is increased in size and lipophilicity, ranging from H, CH.sub.3, cyclopentyl, exo-norbornyl, 2-indanyl, cycloheptyl, cyclooctyl, and also piperidinyl, benzyl, 3,4-dimethyoxypenethyl, tetrahydrofufuryl and furfuryl, no dramatic change in in vitro potency is observed.
Likewise, U.S. Pat. No. 4,910,190, issued Mar. 20, 1990 to Bergeson et al. and U.S. Pat. No. 5,194,588, issued Mar. 16, 1993 to Edwards et al. and European Patent Appl. Publ. No. 0195212, inventors Michael Kolb et al., published Sep. 24, 1986, teach that a number of alkyl and substituted alkyl groups are allowable as the side chain groups of the amino acids at the P.sub.3 and P.sub.4 positions. Moreover, elastase inhibitors containing typical N-protecting groups such as acetyl, succinyl, t-butyloxy-carbonyl, carbobenzyloxy, 4-((4-chlorophenyl)sulfonylamino-carbonyl)phenylcarbonyl, and the like have been specifically disclosed.
Several analogs of N-4-(4-morpholinylcarbonyl)-benzoyl!-L-valyl-N-3,3,4,4,4-pentafluoro-1-( 1-methyl-ethyl)-2-oxobutyl!-L-prolinamide in which the chiral center of the P.sub.1 residue has been eliminated are disclosed as prodrugs of elastase inhibitors by Burkhart, J. P. et al., J. Med. Chem., 38, 223 (1995). Applicants have recently discovered acylated enol derivatives of known non-fluorinated elastase inhibitors which are useful as prodrugs of elastase inhibitors or are elastase inhibitors in their own right.